1. Field of the Invention
The present invention relates to a method of manufacturing a tee nut, and especially a tee nut comprising a relatively thin portion to be caulked or flared, which is provided on a forward end of a hollow shaft portion.
2. Description of the Background Art
FIG. 12 is a perspective view showing a conventional tee nut 1, which is of interest to the present invention. The tee nut 1 comprises a shaft portion 2 and a flange portion 3 outwardly extending from a first end of the shaft portion 2, which are integrally made of a metal material. The shaft portion 2 is in the form of a hollow cylinder, which is provided with a female screw threading 4 on its inner peripheral surface. The female screw threading 4 is formed along the entire inner peripheral surface of the shaft portion 2.
On the other hand, the flange portion 3 is provided with two pairs of pawls 5, 6, 7 and 8, which are arranged radially opposite each other on the flange portion 3, extending from the first end toward a second end of the shaft portion 2. These pawls 5 to 8 are formed by upwardly bending parts of the outer peripheral edge of the flange portion 3.
Such a tee nut 1 is fixed to an object such as a timber, for example, by inserting the shaft portion 2 in a hole that has been previously provided in the object, and then driving the pawls 5 to 8 into the object. Upon such fixing to the object, the tee nut 1 is inhibited from rotation so that a screw member such as a bolt can be screwed into and engaged with the female screw threading 4 which is formed on the inner peripheral surface of the shaft portion 2.
Such a tee nut 1 is generally called a "hopper feed tee nut", since the tee nut 1 can be smoothly and automatically fed and moved along a feed track provided on a nut fixing tool for fixing the nut to the object. For example, British Patent No. 1,157,734 describes a type of such a hopper feed tee nut in detail.
FIG. 12 shows the aforementioned feed track 9 in phantom lines. This feed track 9 comprises a pair of guide rails 10 and 11 having C-shaped sections, which are symmetrically arranged to be opposite to each other. The flange portion 3 is received in these guide rails 10 and 11, so that the tee nut 1 is moved along the feed track 9 in a prescribed orientation while locating the pawls 5 to 8 between the guide rails 10 and 11. The feed track 9 may be curved to bring the tee nut 1 into a desired orientation and position, although such a bent state is not shown in FIG. 12, so that the shaft portion 2 is aligned with a hole that has been provided in the object (not shown).
However, a disadvantage of such a conventional tee nut 1 is that its condition of being fixed to the object is maintained substantially only by the pawls 5 to 8 biting into the object. The pawls 5 to 8 may become so loosened from the object over time, that the tee nut 1 can come completely loose and fall out of the object in the worst case. FIGS. 13 and 14 show another conventional tee nut 12, which has been proposed in order to solve such a problem. FIGS. 13 and 14 are a front elevational view and a bottom plan view showing the tee nut 12 respectively.
This tee nut 12 comprises a shaft portion 13 and a flange portion 14 outwardly extending from a first end of the shaft portion 13, which are integrally made of a metal material, similarly to the aforementioned tee nut 1. The shaft portion 13 is in the form of a hollow cylinder and has a portion 15 to be caulked, sprayed or flared at a second end opposite the first end, while a female screw threading 16 is formed on an inner peripheral surface portion excluding the portion 15 to be caulked. The portion 15 to be caulked has a relatively small thickness.
On the other hand, the flange portion 14 is provided with two pairs of pawls 17, 18, 19 and 20, which are arranged radially opposite to each other on the flange portion 14, extending from the first end toward the second end of the shaft portion 13. These pawls 17 to 20 are formed by upwardly bending parts of the outer peripheral edge of the flange portion 14.
Such a tee nut 12 is used in the manner shown in FIG. 15, for example. Referring to FIG. 15, an object 21 such as a timber for example, has previously been provided with a through hole 22. The shaft portion 13 of the tee nut 12 is inserted in this through hole 22. In this state, the portion 15 to be caulked shown in FIG. 13 is splayed open ad flared or caulked by a caulker, so that a caulked portion 15a is formed on one surface of the object 21. At the same time, the pawls 17 to 20 are driven into the other surface of the object 21. Thus, the tee nut 12 is completely fixed to the object 21 from both sides so that it cannot fall out.
In such a mounting state of the tee nut 12, the pawls 17 to 20 inhibit the tee nut 12 from rotation with respect to the object 21, while the flange portion 14 and the caulked portion 15a hold the object 21 to inhibit disengagement of the tee nut 12 from the through hole 22. Thus, the tee nut 12 is strongly fixed to the object 21, and such a fixed state is semipermanently maintained.
This tee nut 12 is also used as a "hopper feed tee nut", similarly to the aforementioned tee nut 1. Therefore, the tee nut 12 can also be moved along the feed track 9 shown in FIG. 12. When a plurality of such tee nuts 12 are moved along the feed track 9, however, the movement is frequently hindered as follows.
The flange portion 14 of the tee nut 12 is substantially in the form of a circle before formation of the pawls 17 to 20. Therefore, the remaining part of the flange extending between the pair of pawls 17 and 18 and the other pair of pawls 19 and 20 has arcuate sides 23 and 24 respectively. When a plurality of tee nuts 12 are serially moved along the feed track 9 (see FIG. 12), the curved sides of the flange portions 14 tend to overlap with those of adjacent tee nuts 12. Consequently, the tee nuts 12 are frequently misfed or jammed along the feed track 9.
On the other hand, the flange portion 3 of the tee nut 1 shown in FIG. 12 is in the form of an octagon as a whole, and the flange edges extending respectively between the two pairs of pawls 5, 6, 7 and 8 have linear sides 25 and 26 respectively. When a plurality of such tee nuts 1 are fed along the feed track 9, the linear flange sides 25 and 26 of the flange portions 3 positively butt against one another and very rarely cause the aforementioned overlapping phenomenon.
Thus, it is expected to be possible to reduce the aforementioned overlapping phenomenon in the tee nut 12 shown in FIGS. 13 and 14 by changing the shapes of the arcuate sides 23 and 24 of the flange portion 14 to a flat or linear shape. However, the arcuate shape of the sides cannot be so easily changed, as hereinafter described, and in practice it is impossible to find such a modified tee nut in the market.
In general, the tee nut 12 is obtained by drawing a longitudinal strip-shaped metal plate. Such a strip-shaped metal plate is fed along a progressive die to be worked in steps in a prescribed order, so that an intermediate product is separated from the strip-shaped metal plate at a stage that must thereafter be subjected to some further working for obtaining the tee nut 12. This intermediate product has portions corresponding to the shaft portion 13 and the flange portion 14, with slits for forming the pawls 17 to 20. The intermediate product is then grasped by a chuck at the flange portion 14, so that the portion 15 to be caulked and the female screw threading 16 can be formed in the shaft portion 13 in this state. The portion 15 to be caulked is formed by cutting the inner peripheral surface of the shaft portion 13 with a cutting tool for reducing the thickness. Thereafter the pawls 17 to 20 are raised up from the flange portion 14, to obtain the desired tee nut 12.
The flange portion 14 is substantially circular shaped at the stage before formation of the pawls 17 to 20 as hereinabove described, so that the circular flange can be grasped in a chuck for machining, i.e. cutting or milling the interior of the shaft portion 13 for obtaining the portion 15 to be caulked. If the flange portion 14 to be grasped by the chuck has a substantially circular shape, it is possible to grasp the flange portion 14 in the chuck while properly centering the shaft portion 13, since the flange portion 14 has no directivity with respect to such chucking. In this case, further, the flange portion 14 has no corners along its outer periphery, whereby no flash is caused by the chuck grasping the flange portion 14 since no part of the outer periphery of the flange portion 14 will be crushed.
On the other hand, it is difficult to grasp the flange portion 3 having a substantially octagonal shape as shown in FIG. 12 in a chuck due to its directivity, while it is also difficult to center the shaft portion 2. When the flange portion 3 is grasped by a chuck, corners of the flange portion 3 may be compressively deformed to result in flashes. Such flashes inhibit the tee nut 1 from smoothly moving along the feed track 9. While a chuck having a special configuration may be employed in order to solve the aforementioned problem, it would then be necessary to uniformly insert each flange portion 3 of each tee nut into the chuck in a particular orientation, which results in a complicated operation.
In the tee nut 12 having the portion 15 to be caulked as shown in FIGS. 13 and 14, therefore, the flange portion 14 must be substantially in the form of a circle in a stage before formation of the pawls 17 to 20.